Two-Dimensional Flow Field Visualization of Temperature-Sensitive Magnetic Fluids Using a Luminescent Microcapsule

There has been no study for measuring the comprehensive flow field of magnetic fluids. A pumpless transport system has been envisaged based on the temperature dependence of the magnetization of magnetic fluid; however, the knowledge regarding the internal flow is still limited. It is difficult to optimize the design and realize the practical use of the transport system using magnetic fluid. Therefore, in this study, for the first time, a two-dimensional flow field was visualized by encapsulating a magnetic material in a microcapsule and labeling it with fluorescence. The flow field was measured with high accuracy using a fluorescent capsule, and the effectiveness of this method was demonstrated. When a magnetic field was applied, the location of the velocity peak shifted toward the magnetic field. Chain clusters were generated and gathered on a wall. The clusters maintained their shape and slid on the wall owing to the fluid shear force. At high temperatures, the capsules did not form clusters, and there was no change in peak velocity. In a previous study, it was shown that the heat transfer efficiency of magnetic fluids increases when a magnetic field is applied. In this study, it was suggested for the first time that the clusters generated on the wall promoted heat transfer on the wall, and the wall velocity could induce a change in the temperature boundary condition. The results of this study can help elucidate the flow characteristics of magnetic fluids and optimize the device design of the transport system using magnetic fluid.